Any West End theatre wanting to mount a production of Cinderella, the Pied Piper of Hamelin or the Nutcracker Suite won't have far to look for the furry co-stars: according to a whisker-twitchingly gruesome survey by the actors' union Equity, three-quarters of theatreland is infested with mice, rats and fleas.

Perhaps the most shuddery response was from an anonymous actor who left makeup on her dressing table after a show: "I had tiny bite marks on my lipstick recently when I left the lid off."

Another reported: "We see and hear mice. They eat through food packaging and even through one of the girl's warm-up tops."

"Our floors have been eaten by mice," another said, "and they leave their faeces."

And yet another lamented: "Mice, mice, mice. Quite often there is an unpleasant smell which usually turns out to be a dead one."

Christine Payne, the general secretary of Equity, said she expected bad news, but was shocked by the responses. The union surveyed actors and stage managers separately, but the responses were identical.

"These findings mean that tonight over 600 actors and stage managers will go to work knowing that they will probably see and smell vermin, both living and decomposing, in their workplace.

"I accept that many West End theatres are old and difficult buildings to manage, but this is running out of control. These appalling conditions must come to an end."

The respondents said backstage areas were mostly clean and tidy, but there were complaints that only half the theatres have a clean area for preparing the food and drink that actors have to consume on stage in many shows.

Few performers had access to a green room for relaxing, or to prepare food for themselves between shows: on matinee days the gap between many afternoon and evening shows can be as short as an hour.

At this stage Equity is not naming names, but the respondents work in some of the most famous theatres and long-running shows in the world, including The Phantom of the Opera at Her Majesty's Theatre, Oliver! at the Theatre Royal Drury Lane, Billy Elliot at the Victoria Palace and Blood Brothers at the Phoenix.

Many of the buildings look glamorous to audiences, but are Victorian or Edwardian structures on cramped sites, with up to five floors built below street level, deep into London's underworld of tube tunnels, sewer pipes and buried rivers. Previous reports for the theatre-owners and the Theatres Trust suggest the bill for upgrading and modernising the buildings would run into hundreds of millions.

"We're not underestimating the difficulty of it, or saying how it can be done," said Martin Brown of Equity. "We're a trade union, not rat-catchers. What we are saying is that there is no other group of workers in the world expected to go to work night after night in these conditions, and it cannot be beyond the wit of man to devise a solution.

"Perhaps a theatre cat or two might not go amiss – a fine old theatre tradition that seems to have fallen into disuse of late."